Automatic headlight control



Jan. 3, 1956 D. J. PSORAS EI'AL 2,729,767

AUTOMATIC HEADLIGHT CONTROL Filed Jan. 7, 1953 F] E. Z

IN V EN TOR5. DEN/v15 YT/T5012 5. WAL TEE C. 52 omv.

United States Patent AUTOMATIC HEADLIGHT CONTROL Dennis J. Psoras and Walter C. Brown, Baltimore, Md.

Application .lanuary 7, 1953, Serial No. 330,060

5 Claims. (Cl. 315-83) This invention relates to automatic electric control systems, more particularly to systems for changing multibeam headlights from bright to dim in response to light from an approaching vehicle.

In order to dim the headlights of. an automobile, it is generally necessary to depress a foot-switch of some type. The inconvenience of this operation leads to failure of many motorists to dim their headlights upon nearing an oncoming vehicle and not infrequently results in trafl'ic accidents. The need for an eificient, simple, and practical automatic apparatus for performing this operation has long been experienced, but the systems of the prior art have been inadequate in both a technical and practical aspect. The present invention offers a definite solution to the problem of automatic headlight dimming.

Accordingly, it is an object of the invention to provide a new and improved system of headlight control.

It is a further object of the invention to provide a headlight control system which is completely automatic, but with adaptation for manual control when desired.

Another object of the invention is to provide an electronic system for dimming headlights upon nearing an oncoming vehicle, and for returning the headlights to their bright condition when the oncoming vehicle has passed.

It is an additional object of the invention to provide an automatic, photoelectrically actuated control system which has improved sensitivity and stability. These and other objects of the invention will more clearly appear from consideration of the following specification in conjunction with the accompanying drawings, wherein:

Fig. 1 is a block diagram of the system of the invention; and

Fig. 2 is a schematic diagram of the circuit of the automatic control unit.

Referring to Fig. i, designates a standard headlight having a high beam or bright filament 11 and low beam or dim filament 12. Power is supplied from the conventional 6 volt automobile battery 13, which in the embodiment shown has its positive terminal grounded. The negative terminal of the battery is connected through an ammeter 14 to the headlight switch 15 and then to an input terminal of the automatic control unit, generally designated 16. interposed in the circuit connecting the lamp filaments to the control unit is the conventional dimmer foot-switch 17. An auxiliary override switch 18, which normally provides a ground connection for the control unit 16 may be actuated manually to disable the control unit by breaking the ground connection.

Referring now to Fig. 2, the control unit 16 comprises a twin discharge device or vacuum tube 19 having two triode sections 20, 21, comprising anodes 22, 23, control grids 24, 25, cathodes 26, 27, respectively, and if desired, having a grounded grid 28 to isolate the sections of the tube. Plate potential is supplied from the battery terminal through a conventional vibrator 29, center-tapped vibrator transformer 30, and rectifier 31. The vibrator is operated with its movable element grounded through the override switch and its stationary contacts connected to the negative battery terminal through the primary of transformer 30. The output from rectifier 31 is filtered by a network comprising resistor 32 and electrolytic condenser 38, and is applied to anode 22 through the field 34 of a relay which includes armature 35 and contacts 36, 37 connected to high and low beam terminals, respectively (as in Fig. 1). Electrolytic condenser 38 prevents chatter and ensures smooth operation of the relay.

Plate potential for triode 21 is obtained from a voltage divider comprising resistors 39, 49, and 41. Cathode 27 is directly connected to grid 24 and is connected to ground through a high resistance 42. The grid 25 is connected to anode 23 through a photoelectric tube 43 having a photocathode 44 and a collector or anode 45. The phototube 43 has a very high resistance in its dark state and a relatively low resistance when exposed to light of suficient intensity. Since the grid 25 is not provided with a grid leak resistor, it is substantially floating or isolated when the phototube is in its dark state.

The filament or heater 46 of tube 19 may be energized from the battery as indicated, and a fuse 47 may be included for overload protection.

An important feature of the invention is the provision of condenser 48, which is connected between one contact of the vibrator 29 and the grid 25. This condenser has a small capacitance and if the circuit is properly constructed, may if desired, be constituted by the distributed capacity of the leads. its function is to ensure positive blocking of triode 2i and to provide a sensitivity control as will more fully appear below.

Operation of the circuit Assuming that the light switch 15 has been closed and the override switch is is in position to provide automatic operation, control unit 16 will be energized from the battery 13. Operation of the vibrator 29 will provide suitable potentials for the tube 19 and the phototube 43. The essentially square wave signal from the vibrator 29 is applied to the grid 2 through capacitor 48 and there serves to increase the negative potential when the triode 21 is non-conductive. This is accomplished due to the fact that the positive alternations attract a surplus of electrons to the grid 25 to supplement those stored there; blocking triode 210 in the absence of light of suificient intensity impinging upon the photocathode 44.

When triode 21 is in a blocked condition, there exists no potential difference across resistor 42. Therefore grid 24 of triode 2% is at ground potential. The cathode 26 is held at a potential positive with respect to ground by voltage divider resistors 32, 46, and ii. Triode 20 is thus non-conducting because of the cathode bias. in this condition the pull of the relay field 34 is insufficient to move the armature 35, which is normally biased toward contact 36 by a spring (not shown), and the headlights are on high beam.

When light of sufficient intensity from the headlights or an oncoming vehicle impinges upon the photocathode 44, the normally high resistance of the photocell 43 is greatly reduced, effectively unbiocking triode 21. Conduction of the triode 21 developes a positive potential across resistance 4-2. The grid 24 is then made positive in respect to ground, detracting from the potential at cathode 26. Triode 2% then conducts strongly, and the plate current is suiiicient to move armature 35 to contact 37, thereby placing the headlights on low beam. When the approaching vehicle has passed, the photocell 43 regains its high resistance and the circuit reverts to its former condition.

If it is desired to disable the automatic control unit 16,

it is only necessary to operate the override switch 18,

thereby isolating the vibrator 29 from ground and at the same time breaking the cathode return circuit of triode 20. In this condition armature 35 will remain on contact 36, and the headlights will remain on high beam unless the dimmer switch 17 of Fig. 1 is operated. It should be noted that operation of dimmer switch 17 will vary the headlights between high beam and low beam even when the control unit 16 is energized. However, once the control unit has switched the headlights to low beam, operation of the dimmer switch will no longer change the headlights to high beam unless the override switch 18 is operated to deenergize the control unit.

The inclusion of condenser 45 ensures positive blocking of the triode 21 and in addition provides a sensitivity control. By varying this condenser the amount of bias applied to grid 23 may be varied and consequently the light intensity suificient to unblock triode 21 may be set at any predetermined level. It is evident that the spring tension on armature 35 is also a sensitivity control. The phototube 43 may be provided with an optical system and light housing as described in the above-cited copending application.

The embodiment described above is merely illustrative of the principles of the invention, and the invention should not be construed as limited to such an embodiment. Various modifications will appear evident to those skilled in the art.

What is claimed is:

1. A photoelectric control system comprising a discharge device including two triode sections, one section having a cathode, a control grid, and an anode, means for applying a potential to said anode positive with respect to the potential of said cathode; a phototube connected between said grid and said anode, said grid being substantially isolated from said cathode and anode except for said phototube, and capacitor means for coupling a blocking potential to said grid.

2. Switching apparatus comprising a first discharge device having a cathode, a control grid and an anode, a second discharge device having a cathode, a control grid and an anode, an output circuit coupled to the anode and cathode of said first discharge device, the grid of said first discharge device being connected to the cathode of said second discharge device, light responsive means for connecting the grid of said second discharge device to the anode of said second discharge device, said last-mentioned grid being substantially floating in the absence of light upon said light responsive means, and capacitor means for applying a negative bias to said last-mentioned grid.

3. In a control system, a discharge device having a cathode, a control grid, an anode, condenser and conductor means for applying a negative bias to said grid, and means responsive to light for connecting said grid to said anode, said grid being substantially isolated from said cathode and anode except for said light responsive means.

4. Apparatus for varying a lamp between bright and dim conditions, comprising a first triode, a second triode, the grid of said first triode being connected to the cathode of said second triode, plate potential supply circuits connected to the plates of the respective triodes, a lamp operable in bright and dim conditions, means responsive to changes in plate current of said first triode for switching said lamp between bright and dim conditions, a phototube having its cathode connected to the grid of said second triode, and its anode connected to the anode of said sec ond triode, and capacitor means for applying a blocking bias to the grid of said second triode.

5. A system for photoelectric control comprising first and second vacuum tubes each having an anode, a cathode, and a control grid, means for varying the conductivity of said first tube in response to the conductivity of said second tube, a phototube connecting the grid and the anode of the second tube, said last-mentioned grid being substantially isolated except for said phototube, condenser and conductor means for applying a blocking bias to said last-mentioned grid, a source of operating potential for said vacuum tubes and said phototube, an anode-cathode circuit for said first tube including a relay, and means for disabling said source of potential and for interrupting said anodecathode circuit.

Ramberg, New York, John Wiley and Sons, Inc., 1949, pages 229-230. 

